Machines, for example, motor graders, dozers, compactors, pavers, and profilers to name a just a few, are used for geographic surface altering operations. Such machines typically operate at construction sites which were previously manually surveyed, and staked according to construction site plans. During the process the construction site is frequently checked in order to confirm that the processed site meets the design specifications. This process requires large amounts of manual labor much of which is by highly trained personnel. Further, the machine operator must be highly trained in order to obtain the degree of accuracy required.
Laser systems have been in used in some applications to provide a reference for the operator to follow. A laser beam emitted by a laser positioned at a surveyed location on the site is swept over the site. This establishes a laser plane. A receiver on the machine receives the laser beam and indicates to the operator the elevational position of the beam relative to a location on the machine, such as the machine or implement. This information is used by the machine operator for machine controlling purposes. An example of one such system is shown in U.S. Pat. No. 4,807,131 dated Feb. 21, 1989, to Philip M. Clegg. This patent discloses measuring the elevational position of the grading blade relative to the laser plane and displaying on a monitor parameters such as target elevation, actual elevation, and an allowable range of error so that the operator can, in one mode of operation, adjust the blade position to be within tolerance of the target location.
Implements are normally adjustably connected to the machine frame so that the slope, pitch, and elevation of the work implement can be varied relative to the machine. When the laser receiver is mounted on the machine frame any change in the position of the work implement relative to the frame causes an unaccounted for change in the position of the work implement relative to the plane and the receiver. The information therefore provided to the operator is less than desirable and may not be used to any significant advantage. Placing a single laser receiver on the work implement eliminates this problem to the extent that the laser receiver moves with the work implement and is related to work implement position. However, any changes in tilt, pitch or rotation of the work implement relative to the laser plane are not compensated for and therefore the information provided is still not accurate. Placing two laser receivers on the implement permits the slope of the blade to be determined relative to the laser plane however this does not allow for the change in position of the implement caused by implement tipping (pitching).
Systems are known which use a constellation of satellites and a special receiver to determine by triangulation the position of a machine (actually the position of the receiver) in three space coordinates relative to a work site coordinate system. Such systems are normally referred to as a kinematic global positioning systems (GPS). Historically, such systems have not been widely accepted since the accuracy of position determination was less than satisfactory for certain applications. Further, slow processing time reduced the commercial feasibility of determining machine position in realtime. Over the past few years the accuracy of position determination has been improved and the speed of processing has been increased. Thus, the potential to determine the realtime position of a machine is now feasible for an assortment of applications including, for example, geographic surface altering machines.
It is desirable to utilize a global positioning system to determine the realtime position of the work implement, for example, the cutting edge of a geographic surface altering implement. By placing a GPS receiver on the work implement it would appear that the location of the cutting edge could be measured. However, after a closer look, the inability to deal with the dynamics of the work implement and accommodate variations in work implement orientation relative to the frame, for example, pitch of the work implement makes such a modification impossible.
Any GPS receiver mounted on a work implement must be spaced from the cutting edge because of the harsh environment in which the implement operates. Since the GPS receiver determines the position of the antenna of the receiver in space and not the position of the cutting edge, any variations in the orientation of the work implement, such as discussed above, reduces the possibility of being able to accurately determine the cutting edge position. For at least the above reasons placement of a GPS receiver on the work implement would not be considered.
In some applications the accuracy of determining the coordinate position of a work implement relative to a work site using a GPS receiver is less than required to meet acceptable standards. The measurement accuracy in the elevational direction of the site coordinate system is particularly important in applications where the end product is a finished surface, for example, a road way surface. Attempts to address this problem are being made but have not resulted in an accurate enough GPS.
The present invention is directed to overcoming one or more of the problems as set forth above.